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In: Chemistry

Propose a detailed, step-by-step procedure for making 100-mL buffer solutions from the following: 0.100 M NaCH3CO2...

Propose a detailed, step-by-step procedure for making 100-mL buffer solutions from the following: 0.100 M NaCH3CO2 and 0.100 M HCH3CO2 0.100 M HCH3CO2 and 0.100 M NaOH

Expert Solution

Follow the steps given below to prepare the buffer solution.

Step-1: Determine the required pH and concentration of the buffer solution to be prepared. Suppose 'M' be the concentration of the buffer.

Step -2: Now find the sum of the moles of CH3COO-(aq) and CH3COOH in the buffer solution by multyplying volume of buffer solution(0.100 L) and concentration of buffer solution(M). Hence

moles of CH3COO-(aq) + moles of CH3COOH = MxV = M x 0.100L = 0.100M mol ------ (1)

Step-3: Find out the ratio of the concentration of CH3COO-(aq) and CH3COOH applying Hendersen equation

pH = pKa + log([CH3COO-(aq)] / [CH3COOH])

Since the volume of buffer(100mL) remain same for both the CH3COO-(aq) and CH3COOH, the concentration ratio will also be equal to mole ratio of CH3COO-(aq) and CH3COOH. Suppose the molar ratio be 'X'

moles of CH3COO-(aq) / moles of CH3COOH = X ------ (2)

Step-4: Now consider the moles of CH3COO-(aq) be 'Y' mol.

Hence moles of CH3COOH = (0.100M mol - Y) (From eqn-1)

Step-5: Now solve equation (1) and (2) to get the value of 'Y'

From the value of 'Y' we can find out the moles of CH3COO-(aq) and CH3COOH need to beadded.

Step-6: Now find out the volume of 0.100 M NaCH3CO2 and 0.100 M HCH3CO2 from the relation

moles of CH3COO-(aq) or CH3COOH= MxV

=> V of CH3COO-(aq) or CH3COOH = (moles of CH3COO-(aq) or CH3COOH) / M

Step-7: Now measure the calculated volume of stock solution of 0.100 M NaCH3CO2 and 0.100 M HCH3CO2 and add them to prepare the buffer of the required pH.

Step-8: Add 0.100 M NaOH to neutralize any extra CH3COOH added and to get the exact pH.

queen_honey_blossom answered 2 years ago

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